1. Field of the Invention
The present invention relates to a wired circuit board and, more particularly, to a flexible wired circuit board with a metal substrate having a shield layer formed thereon.
2. Description of the Prior Art
Along with an increasing demand for size reduction and high integration of an electric device or an electronic device in recent years, required qualities for a flexible wired circuit board with a metal substrate, such as, for example, finer pattern of the wired circuit and higher thickness precision constituent material, are increasingly becoming severe.
The finer the wired circuit pattern becomes, the higher and weaker the signal frequency becomes particularly in a suspension board with circuit to be mounted on a hard disk drive, so that influence of noise on the signal is increasingly becoming noticeable.
For reduction of noise, proposals have been made such as, for example, arranging a ground wire in the vicinity of the wiring pattern, or widening space between wires of the wiring pattern. However, these proposals are not sufficient for the noise reduction required in these days.
Accordingly, a further proposal has been made for covering an insulating cover layer that covers the wiring with a conductive shield layer in order to achieve the currently required significant noise reduction.
For example, Japanese Laid-open (Unexamined) Patent Publication No. 2003-69170 proposes improvement of a printed board comprising (i) a signal conductor and (ii) a ground conductor extending along the signal conductor, which are formed on a substrate in the form of wiring pattern, and (iii) an insulating layer to cover the wiring patterns, wherein a non-insulating section is formed in the insulating layer to expose a part of the ground conductor therefrom, and also a conductor layer is formed to cover the insulating layer over the signal conductor and is brought into conduction with the ground conductor via the non-insulating section, so that unwanted radiation is reduced.
Also, in the suspension board with circuit, when a conductive shield layer is formed to cover the insulating cover layer by plating or the like so as to be electrically connected to the metal substrate, the effect of significant noise reduction can be provided.
However, JP Unexamined Patent Publication No. 2003-69170 cited above has the disadvantage that since the conductor layer is formed by a conductive tape or film, the conductor layer strips off too easily.
On the other hand, in the suspension board with circuit mentioned above, when the shield layer is formed by plating or the like, the shield layer is well contacted with the insulating cover layer, but is poorly contacted with the metal substrate, so that the shield layer strips from the metal substrate gradually from an end thereof.